The present invention relates generally to optical transmission and reception devices and packages, and particularly to an optical assembly which significantly relaxes tolerances of one device relative to another while maintaining high coupling therebetween.
Optical communications have gained widespread acceptance for both telecommunications (telecom) and data communications (datacom) applications. Moreover, the telecom and datacom applications are often digital optical communications systems. Telecommunication systems may operate over single-mode fiber at distances from approximately 10 km to approximately 100 km and greater, and employ lasers which emit light at wavelengths of approximately 1310 nm to approximately 1600 nm. Data communications systems may cover shorter distances of up to a few kilometers, and may use multi-mode fiber. Data communications systems can employ laser devices as well, typically having emission wavelength of approximately 600 nm to approximately 850 nm.
As the transmission and reception rates in the telecom and datacom industries continue to increase, there are ever increasing demands placed on the various components of the optical communication system. In addition, many of these demands are further complicated by the need to manufacture these components on large scale, while maintaining required accuracies and performance. One such demand placed on optical components is the efficient coupling of power between optical waveguides and optical devices; such as between a laser or amplifier, and an optical fiber. Known techniques to improve the coupling between a laser and an optical fiber include the use of a micro-lens on the end of the fiber to match the modes of the laser and the optical fiber, and the use of bulk optics or a combination of micro-lenses and bulk optics.
While the use of various types of lens elements have generally improved the ability to couple an active device such as a laser to an optical wavguide, there are certain drawbacks to conventional approaches including compromised performance and difficulty of manufacture. To wit, in most optical system designs, the laser is ideally located on an optic axis of the optical waveguide and the coupling elements therebetween. In practice, however, the active area of the active device may not be located on this optic axis. In the example of a laser, when the active area of the laser is not located on the optic axis in conventional optical systems, the achievable coupling is reduced, often to unacceptable levels.
The source of the offset may arise from the combination of a number of tolerances. Such tolerances may include the thickness of the semiconductor laser chip, the thickness of any bonds or contacts used therewith, and the tolerances in the thickness of other piece parts. For purposes of illustration, these tolerances can result in a height offset of active area the laser with respect to the optic axis of the system being on the order of approximately xc2x115 xcexcm or more. In conventional optical systems, such an offset will result in unacceptable loss of achievable coupling.
As described, in conventional optical systems an offset of the active device will result in the focusing of the beam on the image plane (x-y plane) of the optical fiber at a position removed from the optic axis. Moreover, the beam may be at an angle with respect to the optic axis. This angular deviation in the image plane of the optical fiber is proportional to the laser offset from the optic axis.
One conventional method used to improve the coupling to the optical fiber requires active alignment of the fiber. This technique may employ x-y-z positioning and angular alignment of the fiber. While this method may be beneficial, it nonetheless complicates the alignment process, and requires a more complicated design. Accordingly, this conventional angular alignment technique is not practical to implement in larger scale manufacturing as it is complex and costly.
Another conventional technique which has been employed to reduce the offset tolerances of an active device is to bond the active layer of the device to a reference plane (e.g. a substrate). This is often referred to as bonding the active region of the active device xe2x80x9cdown.xe2x80x9d However, for various reasons, it is advantageous to bond the active device with the active region xe2x80x9cupxe2x80x9d, and thereby not bonded to the reference plane.
Accordingly, what is needed is a technique for improving the coupling between optical devices which overcomes at least the drawbacks of conventional approaches described above.
In accordance with an exemplary embodiment of the present invention, an optical apparatus includes a first optical element, a second optical element, and a third optical element disposed between the first and second optical elements. Light from the first optical element is incident upon the second optical element at an angle with respect to the optic axis that is substantially independent of an offset of the first optical element in a direction orthogonal to the optic axis.